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Transcript
ElectroRetinoGraphy
Jahanzeb ee-01083-045
Fatima Rafique ee-01083-128
What Is An ERG
•Electroretinography (ERG) is an eye test used to detect
abnormal function of the retina (light detecting portion of
eye)
•It measures the electrical response of the light sensitive
cells such as rods and cones
Biological Basis Behind
The Eye
The eye consists of 3 layers
-Outer Fibrous Tunic
sclera,cornea,limbus
-Middle Vascular Tunic
Iris,Ciliary body,,choroid
-Inner Nervous Tunic
Retina
Eye Structure
First To know About Retina
It is delicate two layered membrane
1. Pigmented Layer : which absorb light and
prevent it from scattering
2. Neural Layer : which contains photorecptors to
transduce light energy
The photorecptors are
1. Rods : respond to dim and bright light
2. Cones: respond to colors
Retinal Layer
How Is An ERG Done??
How is an ERG done??? (Cont)
Usually the patient's eyes are dilated beforehand with
standard dilating eye drops. Anesthetic drops are then placed
in the eyes, causing them to become numb.
How is an ERG done??? (Cont)
An electrode is gently placed on each eye with a device
very similar to a contact lens. An additional electrode is
placed on the skin to provide a ground for the very faint
electrical signals produced by the retina.
During an ERG recording session, the patient watches a
standardized light stimulus, and the resulting signal is
interpreted in terms of its amplitude (voltage) and time
course.
Equipments
Electrodes
Light Simulators
Software to Interpret the results in form of graph
Electrodes
The electrodes measure the electrical activity of the retina in
response to light. The information that comes from each
electrode is transmitted to a monitor where it is displayed as
two types of waves, labeled the A waves and B waves.
Several types of electrode used are
1.speculum structure
2.Gold mylar tape
3.Jet
4. DTl
Types Of Electrodes
Light Simulators
Two Type of light simulators are used in test
Strobe light source (Mobile and simple)
The Ganzfeld Simulation Globe(Best control of intensity)
Complete System
How are eletroretinography readings
made?
Readings during eletroretinography are usually taken first
in normal room light. The lights are then dimmed for 20
minutes, and readings are again taken while a white light
is shined into the eyes. The final readings are taken as a
bright flash is directed toward the eyes.
Why is an ERG done?
An ERG is useful in evaluating both inherited (hereditary)
and acquired disorders of the retina. An ERG can also be
useful in determining if retinal surgery or other types of
ocular surgery such might be useful.
Some of the disorders, which can be predicted by an
abnormal ERG are
choroideremia
Retinitis Pigmentose
gyrate atrophy of the retina
Goldman-Favre syndrome
Now What is Normal ERG??
A normal ERG shows a normal A- and B-wave pattern
with appropriate increases in electrical activity with
increased light intensities.

A-wave : Both rods and cones contributes to it. This is produce due
to the hyper-polarisation of rod and cones
B-wave : The b-wave is generated by ON and OFF bipolar cell (B)
activity, probably containing contributions from the glial Müller cells (M).
Ergs Conclusions
The Graph below show some of the ERG sketch of the
patients effected with mentioned dieases. From the graph
you can see that 1st graph is of normal person and the 2nd
one is of the effected person. The deviation of grapgh from
the normal one shows the presence of disorders.
Ergs Conclusions
Inhereted Disorder
Factors Effecting ERG Waves
Types of electrode
• Wavelenght of Stimulus
• Intensity of stimulus